Mix 1/4 cup of the parsley with next four ingredients; take out half of mixture and to it add rest of parsley; set aside.
Toss remainder of mixture with potatoes and celery.
Combine mayonnaise, dressing, seasonings; add to salad.
Toss.
Pack lightly into 8x8x2-inch pan or shallow 2-quart baking dish.
Sprinkle reserved parsley mixture on top.
Chill.
Lift out servings with pancake turner.